The effects of drugs on smooth muscle strips of human taenia coli, obtained from operation specimens, were studied in vitro. Both nicotinic and
muscarinic sites of action of
acetylcholine were demonstrated, the
nicotinic effect being a relaxation. The
sympathomimetic amines,
adrenaline,
noradrenaline, and
isoprenaline produced a relaxation of the tissue by an action on
adrenaline alpha- and beta-receptors. The presence of both types of receptor was demonstrated by selective
adrenergic blockade with
pronethalol or
Hydergine.
Pronethalol in high concentrations gave a nonselective
adrenergic blockade. The
ganglion-stimulating agents
nicotine and
dimethylphenylpiperazinium produced a relaxation of the tissue in all concentrations. This relaxation was inhibited by
pronethalol or
physostigmine but no contractile component to
ganglion stimulation was revealed when these two drugs were present together. These results indicate the presence of either sympathetic ganglia in the intrinsic nerve plexuses, or
adrenergic stores in the bowel wall. There is no pharmacological evidence for parasympathetic ganglia in human sigmoid colon.
Histamine produced relaxant, contractile or biphasic responses. The type of response was independent of the "tone" of the preparation. The responses were not modified by
procaine,
hyoscine or
pronethalol, which result indicates that both the contractile and relaxant responses to
histamine were due to a direct action of the
drug on smooth muscle.
5-Hydroxytryptamine produced either a contraction or a relaxation of the tissue. The relaxation was due to a direct effect of the
drug, since
hexamethonium,
procaine or
pronethalol did not affect the response. No conclusions have been drawn regarding the mechanism of the contractile response to
5-hydroxytryptamine. The nature of the responses of the tissue to drugs was independent of the disease for which the specimen of colon was removed.